Biologists study how Ohio’s forests respond to climate change

By Andrea Gibson

Each time it rains, the soil chemistry of the forest changes. The effect can be especially pronounced in regions such as southeastern Ohio, where a high number of coal-fired power plants emit sulfur dioxide and nitrogen oxides into the air, creating what's known as "acid rain."

DeForest received funding from the National Science Foundation to study the soil dynamics of two different forests in eastern Ohio to determine how life—from the tiniest microbes to the tallest maple trees—survives such climate change.

Jared DeForest (Photo by Robb DeCamp)

Acid rain fertilizes the soil with nitrogen and reduces the level of phosphorus. Scientists speculated that the microbes in the soil—DeForest compares them to "first responders"—mitigate the change in soil chemistry by producing phosphatase enzymes. The microbes feed phosphorus to forest plants, which reciprocate by providing energy to the microbes.

To test the theory, DeForest and colleagues at the Holden Arboretum and Case Western Reserve University spread experimental treatments of lime, phosphorus, and a combination of the two materials over 72 plots in a forest in Athens, Ohio, and land in northeastern Ohio. Each plot is 800 meters square (20 meters by 40 meters). It took between 12 and 17 tons of lime to neutralize the effect of acid rain, he notes, though only half a ton of phosphorus was needed to mitigate any phosphorus limitation for the entire experiment.

"We had to add enormous amounts of lime just to get the soil chemistry back to the way it was 100 years ago," says DeForest, an assistant professor of environmental and plant biology.

One year later, the researchers observed that the soil microbes reduced their enzyme production in the presence of the added phosphorus, but only in the southeastern plots. These plots feature unglaciated soil that has been more heavily impacted by acid rain than the more fertile, glaciated northeastern plots. DeForest notes that the microbes adapted to the changing soil composition relatively quickly, in a matter of only months.

When DeForest and his student researchers began studying other elements of the forest ecosystem, they were surprised to discover that the maple leaves gathered from the canopy in the experimental plots were "starved for phosphorus," he says. Compared to samples from forest plots that received no treatment, the leaves had 75 percent more phosphorus, which suggests that the soil microbes are falling short of supplying these needed nutrients. DeForest now hopes to learn how this phenomenon influences tree growth and reproduction.

The findings from the scientist's four-year study on the overall ecosystem could have implications for how the U.S. Forest Service manages the forests, including its proactive burning of maples and beeches to regenerate white oaks.

"A lot of effort goes into keeping the forests the same way they were 50 years ago, but we're having a hard time doing it," DeForest says.

The research may bolster the idea that climate change has a much more complicated impact than previously believed, he adds, noting that there are both ecological "winners and losers" in the forests.

This article appears in the Spring/Summer 2012 issue of Ohio University's Perspectives magazine.

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